Nowadays, mobile terminals such as mobile (cellular) phones, personal digital assistants (PDAs) or communicators have many different functions in addition to the conventional one, i.e. to serve as a means for mobile telecommunication of speech between a user of the mobile terminal and another user of a remote device. Examples of such additional functions include camera functionality (involving for instance the capturing of still images or recording of video), audio functionality (involving for instance playback of locally stored or remotely downloaded music), and electronic messaging functionality (such as short message services (SMS), multimedia messaging services (MMS) or email).
As is familiar per se, not all such functionality of mobile terminals is suitable for use everywhere. For instance, use of the terminal's cellular radio interface may be prohibited in hospitals or onboard airplanes. Likewise, camera use may be prohibited in restricted areas such as military bases, corporate premises or at concerts. Audio playback may be prohibited in libraries or at cinemas, etc.
WO2005/002263 discloses a method for temporarily preventing a certain function of a portable device, such as a mobile terminal. Upon receipt of a blocking key via cable, over a wireless link or in an electronic message, a certain function is blocked in the portable device. The certain function may for instance be a camera function. When subsequently receiving an unblocking key, the certain function may be reactivated in the portable device.
More recently, mobile terminals have been developed and introduced which not only have a first wireless interface that permits cellular communication of speech, video or data in a mobile telecommunications network, but in addition a second wireless interface for communication without the use of said mobile telecommunications network.
The first wireless interface is typically adapted for cellular communication in compliance with mobile telecommunication standards such as GSM, UMTS, D-AMPS, CDMA2000, FOMA or TD-SCDMA performed in one or more frequency bands such as 900 MHz, 1800 MHz or 1900 MHz.
The second wireless interface may typically involve short-range supplementary data communication such as Bluetooth at 2.4 GHz, or GPS services. Another example is WLAN (Wireless Local Area Network) access, which is sometimes referred to as Wifi. In the year 1997, the Institute of Electrical and Electronics Engineers (IEEE) ratified the 802.11 specification [IEEE Std 802.11 (ISO/IEC 8802-11: 1999)] as a standard for wireless LANs. IEEE 802.11 enables mobile stations to communicate through a wireless network interface directly with each other or with other stations through an access point. An access point is a centralized gateway providing message and power management and access to an external LAN and/or the Internet. IEEE 802.11 access products are currently widely sold with personal computers, computer peripherals, print servers, and mobile devices such as laptops or mobile terminals like cellular phones, PDAs and communicators. The operating range of a wireless local area network may be up to a few hundred meters in distance, thereby making it very useful for mobile network access in office buildings, warehouses, hospitals, campuses, train stations, airports and many other public areas.
There are a plurality of different protocols within the IEEE 802.11 standards, using different frequency bands and having varying data transmission speeds for wireless packet data communication. The original IEEE 802.11 standard supported wireless interfaces operating at speeds of up to 2 megabit per second (Mbps) in the 2.4 GHz radio frequency (RF) or microwave band, or more specifically between 2.4 and 2.497 GHz. By using different modulation techniques, IEEE 802.11b raised the data transmission rates to 11 Mbps, while IEEE 802.11a supports up to 54 Mbps transmission rates in a 5 GHz band, or more specifically between 5.15 and 5.875 GHz. Moreover, IEEE 802.11g is developing standards for data transmission rates of 54 Mbps in the 2.4 GHz band.
Alternative wireless LAN technologies are HiperLAN2 (operating in the 5 GHz (specifically 5.4 to 5.7 GHz) U-NII band), WiMAX (Worldwide Interoperability for Microwave Access, which is an IEEE 802.16 standard and typically operates in a frequency band located somewhere between 2.5 and 5.8 GHz), and HomeRF.
The terminologies “wireless local area network”, “wireless LAN” or just “WLAN” are used in the remainder of this document as a general reference to any available technology for wireless data communication, including but not limited to any of the technologies referred to above.
A problem with WLAN is that even if the frequency bands mentioned above are normally unlicensed and therefore freely available in most countries, they may nevertheless be reserved for licensed use, for e.g. governmental or military purposes, in individual countries, or may even be completely forbidden to use in such a country. Therefore, manufacturers of mobile terminals may have to design separate versions of mobile terminals, where the WLAN module has been removed, for sale in such countries. Having to design separate versions has apparent drawbacks in terms of design cost, marketing expenses, and service and repair.
In US 2005/0153692, a method and a system are presented for a mobile terminal having both a first wireless interface for cellular telecommunications and a second wireless interface for WLAN access. In this system, the mobile telecommunications network transmits a broadcast signal to the mobile terminal containing information on available (interworking) WLAN(s) in the current cell of the mobile telecommunications network. If no available WLAN is indicated in the information received from the mobile telecommunications network, the mobile terminal maintains its WLAN interface in an inactive sleeping mode for powersaving purposes. On the other hand, if the signal indicates presence of a WLAN in the current cell, the mobile terminal activates its WLAN interface and causes it to scan for WLAN access points (APs) in the neighborhood. To this end, the broadcasted information may contain data that facilitates for the mobile terminal to connect to the WLAN, for instance data regarding type, identity or frequency channels of the WLAN.
Thus, in the approach of US 2005/0153692, the WLAN interface is normally kept in a sleeping mode, unless information is provided from the mobile telecommunications network to the effect that there is an available WLAN nearby. While this service may have its benefits when it comes to powersaving, it still has some drawbacks.
Firstly, modification of the mobile telecommunications network is required, so that it supports this service. Secondly, if the mobile terminal is used in a mobile telecommunications network where this service is not available (for instance if the terminal is brought abroad and uses roaming), or if the service is simply interrupted for some reasons in a current cell of a network where it would normally be provided, the WLAN interface will be kept in its sleeping mode forever, and the mobile terminal may fail to avail itself of opportunities to WLAN access as they may exist.